Method of tuning telephone-receivers.



H. J. POWER METHOD OF TUNING TELEPHONE RECEIVERS.

APPLICATION FILED FEB. 5, i914.

Patented May 4, 1915.

[1 l. l LLlllIl k II'HIF W/T/VESSES //VV/V7"0R qJ Maw 77 HAROLD J. POWER, OF EVERETT, MASSACHUSETTS.

METHOD OF TUNING TELEPHONE-RECEIVERS.

Specification of Letters Patent.

Patented May 4, 1915.

Application filed February 5, 1914. Serial No. 816,718.

To all whom it may concern.

Be it known that I, HAROLD J. POWER, of Everett, in the county of Middlesex and State of Massachusetts, have invented certain new and useful Improvements in Methods of Tuning Telephone-Receivers, of which the following is a specification.

This invention relates to telephone receivers, and more particularly to those adapted for use in wireless telegraphy and telephony. In such apparatus, to attain the greatest audibility for incoming signals of different frequencies, it is important that the fundamental period of vibration of the receiver diaphragm shall be substantially the same as the particular pitch frequency of the signals which are to be read at the time. This tuning of the receiver I effect through y'ariations in the magnetic tension of the diaphragm, obtained by changing the magnetic flux in or the degree of saturation of the receiver magnet. This result may be attained by altering either the magnetomotive force of the magnetic circuit or its reluctance. The latter variation, either by moving the magnet toward and from the diaphragm or similarly adjusting the diaphragm with respect to the magnet, is too coarse to give an easy and accurate method of tuning, since a slight change in the airgap leads to a very marked change in the,

reluctance of the circuit, and consequently in the flux. Moreover, the reluctance is not only changed by the intended manual variation in the length of the air gap, but also by the incidental automatic variation due to the bowing of the diaphragm under the influence of the adjustment. In tuning for a high pitch frequency a further difficulty is introduced by the fact that the pole of the magnet and diaphragm approach one another so closely that the latter is liable to bow in sufficiently to adhere to the pole, thus rendering the receiver inoperative. I therefore preferably adjust the magnetomotive force, the most satisfactory manner of doing this being to alter the current flowing through a low resistance polarizing winding applied to a core of low retentivity for magnetic flux and placed outside the customary high resistance signaling winding. At the same time I also adjust the air-gap to keep it, and therefore the reluctance of the magnetic circuit, approximately constant and thus avoid the difficulties previously mentioned. By this method of procedure the receiver may be kept at a high state of efficiency as a detector of signals of different pitch frequencies.

In the accompanying drawings I have shown apparatus by which this invention may be carried out Figure 1 being a central vertical section through one form of telephone receiver; Fig. 2 a plan view, partly diagrammatic, of the same instrument; Fig 3 a sectional view of'another form of receiver; Fig. 4 a partly diagrammatic plan view of the same, and Fig. 5 a sectional elevation of a form of receiver in which the reluctance-'ofan. auxiliary magnetic path is varied.

The form shown in Figs. 1 and 2 is an adaptation of the well-known construction of receiver, in which the permanent magnet is replaced by a horse-shoe shaped laminated structure 10, of a metal having low retentivity for magnetic flux, preferably soft iron, having angular pole pieces 12, 14, secured to its ends, the whole being preferably mounted on' a base plate 15. The vertical legs of the pole pieces 12, 14, are surrounded by the usual windings 16, 17, which are connected in series in the usual manner and to binding posts 20, 21., respectively.

Surrounding the windings 16, 17, are lowresistance windings 22, 23, of a relatively coarse wire and a comparatively,small number of turns, and these windings are connectv ed in series. The winding 23 maybe connected'to a binding post 24, and the wire leading from the winding 22 is wound around the yoke 10 to form the winding 26, between the pole pieces 12 and 1.4, and the end of this winding may then be connected to a binding post 28.

A wire 30 is connected to the terminal 28 and to a variable resistance 32, having a movable contact-member 33 for rough or approximate adjustment, which is connected by a wire 34 to a second variable resistance 36. and the latter is intended for accurate adjustment of the strength of current. A movable contact-member 38 engages the resistance element 36, and is connected to one pole of a battery 40, and the other pole of this battery is connected by a wire 41 to the terminal 24. It will be understood that any means for suitably varying the strength of current is within the scope of my invention.

The upper ends 42, 43, ofthe pole pieces 12, 14, or the poles of the magnet, are in proximity to a diaphragm 44, which is seated at the upper edge of the cup-shaped casingmember 4-6, and held in place by the earpiece or cover 48, the latter being screwed onto the casing 46 in the usual manner. Rotatably mounted in the bottom wall 49 of the casing 46 in an adjusting screw 50, which is threaded through the plate 15. By this construction the entire magnet may be raised and lowered to vary the distance'between the diaphragm seat and the poles 42, 48. By moving the magnet poles with respect to the diaphragm seat I can compensate for the inward movement of the diaphragm toward the pole tips upon increasing the strength of the current through my additional winding on the yoke and pole tips. thus keeping the reluctance in the magnetic circuit con- 'stant at all times. This provides a finer regulation of the degree of saturation of the magnet core because its degree of saturation then depends simply on the strength of current sent through the winding on the yoke and pole tips. The extent of movement of the pole tips with respect to the diaphragm seat with increasing current strength may be calibrated as followsz-Set the magnet poles at the minimum distance from the diaphragm seat, which is determined by the design of the receiver parts. and throughout the calibration test leave the poles in this fixed position with respect to the diaphragm seat. Next measure the distance through which the diaphragm bows down for ditterent values of current strength, from its original position with no current flowing through the winding. In this way the proper distance of the pole tips from the diaphragm seat can be determined so that the reluctance of the magnetic circuit can be kept constant for all different values of current strength through the additional winding. From the data of the calibration test the proper distance to move the magnet pole tips with relation to the diaphragm seat for diflerent values of current through the additional winding can be obtained so as to maintain constant reluctance at all times and so provide a finer adjustment of the-pole tips than could be attained it the reluctance varied as well as the current through the additional winding. Were the course of merely varying the air-gap followed, the maximum sensitiveness for high frequencies could not be attained, on account of the great change in flux saturation of the'core resulting from the slightest de' crease in the distance between the pole-tips and diaphragm as the critical point is being reached, which causes the diaphragm to come into contact with the pole-tips when jarred. In my receiver, however, by providing an adjustment whereby the distance between the-diaphragm and pole-tips can be maintained constant, the correct degree of saturation of the cores can be obtained without danger of the diaphragm contacting with the pole-tips; and furthermore it is capable of very minute. adjustn'zent of the flux saturation, because it is possible to vary the strength of polarizing current in small increments, say of one. ten thousandth part of an ampere.

The form of device shown in Figs. 3 and 4 comprises a U-shaped core-piece or yoke 60. which is preferably formed of a bundle of soft iron wires secured to a. supporting plate 62, by means of a clamp 64. the latter being held in place by screws 65. The vertical legs of the core, or the pole tips, are surrounded by the usual windings 6G. 67. which are connected in series in the usual manner and to binding posts 68, 69, respectively.

Surrounding the windings 66, 7 are low resistance windings 70, 7]., of a relatively small number of turns of relatively coarse wire, and these windings are connected in series. The winding 70 may be connected to a binding post 72. and the wire 74 connecting the windings 70. 71. may be wound around the core 60 below the bottom of the regular winding bobbins. as shown in Fig. 3. The other end of the winding 71 may be connected to a binding post 76. and these binding posts may be connected to a current source and means for suitably varying the strength of current. as above set forth. In the ordinary receiver the turns of the wind ing nearest the cores are the chief cause of the change of flux incident to the reception of signals. the effect of the outside turns being relatively unimportant on account of their distance from the cores. But by applying the auxiliary polarizing winding outside the signaling winding, the initial magnetic flux through the cores converges inwardly to said cores and in so doing passes through the entire signaling winding. Hence all the turns of the latter are made effective in producing a change in the magnetization of the cores which results in a great increase in the efliciency of the receiver.

The plate 62 is. arranged to be raised and lowered. as by means of a screw 7 8, which is threaded into said plate and rotatably mounted in the bottom of the receiver casing 80. A diaphragm 44 is seated on the upper edge of the cup-portion 80 of the casing. and is held in place by'a cap or carpiece 48. as already described. By this construction the size and weight of the receiver are greatly reduced over that of the ordinary form of receiver, yet the magnet system may be adjusted as above described to keep the reluctance of the magnetic circuit constant.

In Fig. 5 is shown a receiver which may be adjusted to the maximum degree of sensitiveness for incoming wireless signals of different frequencies, by varying the degree of saturation of the pole tips by diverting more or less of the magnetic lines of force set up in the core by the permanent steel magnet through an auxiliary path. As here shown, the receiver comprises a permanent steel magnet 90, having angular soft iron pole pieces 92, 93, secured to its ends, the whole being suitably supported in a casing 94, containing a diaphragm 44 held in place by a cap 48, as already described. The main magnetic circuit is through the permanent magnet 90, pole-pieces 92, 93, and the diaphragm 44.

The pole-pieces 92, 93 are surrounded by the ordinary windings 95, 97, and are preferably beveled at their angles, and between said pole-pieces a beveled soft iron plate 96 is adjustably mounted to provide an auxiliary path for the magnetic flux and forming with the pole-pieces a pair of air-gaps 98, 99. As shown, the plate 96 is secured to a thin yielding plate 100, mounted upon the bottom of the receiver casing 94 and tendin normally to cause said plate 96 to approach the pole-pieces. An adjusting screw 101 is rotatably mounted in the plate 96 and threaded to receive a nut 102, which bears against the outside of the bottom of the easing 94. By adjusting the soft iron plate 96 with respect to the pole-pieces 92, 93, the air-gaps 98, 99, are varied and the amount of flux or the number of magnetic lines of force passing through this auxiliary path are varied. As the air-gap is increasedby Withdrawing the soft iron plate 96 from between the pole pieces toward the bottom of the receiver shell, the reluctance of the diverting path increased, thereby reducing the amount of flux which is diverted and thus increasing the saturation of the pole cores which are part of the main magnetic circuit. This method of adjustment is an improvement over the method in which the air-gaps of the main magnetic circuit are varied, because-a finer adjustment of the degree of saturation is obtainable, and also because? the main parts of the receiver can be rigidly fixed in place in the best position, as in the case of any ordinary receiver.

lVhat I claim is 1. The method of tuning a telephone receiver to signaling impulses of a particular frequency which consists in varying the degree of saturation of the cores of the receiver magnet and maintaining the reluctance of the ma eticcircuit approximately constant.

2. T e method of tuning a telephone receiver to signaling impulses of a particular frequency which consists in varying the magnetic tension of the diaphragm and the maintaining of the reluctance of the magnetic circuit approximately constant.

3. The method of tuning a telephone receiver to signaling impulses ofa particular frequency which consists in subjecting the receiver magnet to the influence of a polarizing current independent of the signaling current, varying the strength of said current until therate of vibration of the receiver diaphragm corresponds to the frequency of the signaling impulses, and varying the relative position of the pole of the receiver magnet and diaphragm to maintain the air-gap approximately constant.

In testimony whereof I have aflixed my signature in the presence of two Witnesses.

HAROLD J. POWER. \Vitnesses SAMUEL Looms. CHARLES R. HERRICK.

Copies of this patent may be obtained for five cents each, by addressing the. Commissioner. of Patents,

Washington, D. 0; 

